#region Apache License
//
// Licensed to the Apache Software Foundation (ASF) under one or more 
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership. 
// The ASF licenses this file to you under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with 
// the License. You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System;
#if NETSTANDARD1_3
using System.Globalization;
#else
using System.Configuration;
#endif
using System.Reflection;
using System.IO;
using System.Collections;

namespace log4net.Util
{
  /// <summary>
  /// Utility class for system specific information.
  /// </summary>
  /// <remarks>
  /// <para>
  /// Utility class of static methods for system specific information.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  /// <author>Gert Driesen</author>
  /// <author>Alexey Solofnenko</author>
  public sealed class SystemInfo
  {
    #region Private Constants

    private const string DEFAULT_NULL_TEXT = "(null)";
    private const string DEFAULT_NOT_AVAILABLE_TEXT = "NOT AVAILABLE";

    #endregion

    #region Private Instance Constructors

    /// <summary>
    /// Private constructor to prevent instances.
    /// </summary>
    /// <remarks>
    /// <para>
    /// Only static methods are exposed from this type.
    /// </para>
    /// </remarks>
    private SystemInfo()
    {
    }

    #endregion Private Instance Constructors

    #region Public Static Constructor

    /// <summary>
    /// Initialize default values for private static fields.
    /// </summary>
    /// <remarks>
    /// <para>
    /// Only static methods are exposed from this type.
    /// </para>
    /// </remarks>
    static SystemInfo()
    {
      string nullText = DEFAULT_NULL_TEXT;
      string notAvailableText = DEFAULT_NOT_AVAILABLE_TEXT;

#if !NETCF
      // Look for log4net.NullText in AppSettings
      string nullTextAppSettingsKey = SystemInfo.GetAppSetting("log4net.NullText");
      if (nullTextAppSettingsKey != null && nullTextAppSettingsKey.Length > 0)
      {
        LogLog.Debug(declaringType, "Initializing NullText value to [" + nullTextAppSettingsKey + "].");
        nullText = nullTextAppSettingsKey;
      }

      // Look for log4net.NotAvailableText in AppSettings
      string notAvailableTextAppSettingsKey = SystemInfo.GetAppSetting("log4net.NotAvailableText");
      if (notAvailableTextAppSettingsKey != null && notAvailableTextAppSettingsKey.Length > 0)
      {
        LogLog.Debug(declaringType, "Initializing NotAvailableText value to [" + notAvailableTextAppSettingsKey + "].");
        notAvailableText = notAvailableTextAppSettingsKey;
      }
#endif
      s_notAvailableText = notAvailableText;
      s_nullText = nullText;
    }

    #endregion

    #region Public Static Properties

    /// <summary>
    /// Gets the system dependent line terminator.
    /// </summary>
    /// <value>
    /// The system dependent line terminator.
    /// </value>
    /// <remarks>
    /// <para>
    /// Gets the system dependent line terminator.
    /// </para>
    /// </remarks>
    public static string NewLine
    {
      get
      {
#if NETCF
        return "\r\n";
#else
        return System.Environment.NewLine;
#endif
      }
    }

    /// <summary>
    /// Gets the base directory for this <see cref="AppDomain"/>.
    /// </summary>
    /// <value>The base directory path for the current <see cref="AppDomain"/>.</value>
    /// <remarks>
    /// <para>
    /// Gets the base directory for this <see cref="AppDomain"/>.
    /// </para>
    /// <para>
    /// The value returned may be either a local file path or a URI.
    /// </para>
    /// </remarks>
    public static string ApplicationBaseDirectory
    {
      get
      {
#if NETCF
-        return System.IO.Path.GetDirectoryName(SystemInfo.EntryAssemblyLocation) + System.IO.Path.DirectorySeparatorChar;
#elif NETSTANDARD1_3
        return Directory.GetCurrentDirectory();
#else
        return AppDomain.CurrentDomain.BaseDirectory;
#endif
      }
    }

    /// <summary>
    /// Gets the path to the configuration file for the current <see cref="AppDomain"/>.
    /// </summary>
    /// <value>The path to the configuration file for the current <see cref="AppDomain"/>.</value>
    /// <remarks>
    /// <para>
    /// The .NET Compact Framework 1.0 does not have a concept of a configuration
    /// file. For this runtime, we use the entry assembly location as the root for
    /// the configuration file name.
    /// </para>
    /// <para>
    /// The value returned may be either a local file path or a URI.
    /// </para>
    /// </remarks>
    public static string ConfigurationFileLocation
    {
      get
      {
#if NETCF || NETSTANDARD
        return SystemInfo.EntryAssemblyLocation+".config";
#else
        return System.AppDomain.CurrentDomain.SetupInformation.ConfigurationFile;
#endif
      }
    }

    private static string entryAssemblyLocation;

    /// <summary>
    /// Gets the path to the file that first executed in the current <see cref="AppDomain"/>.
    /// </summary>
    /// <value>The path to the entry assembly.</value>
    /// <remarks>
    /// <para>
    /// Gets the path to the file that first executed in the current <see cref="AppDomain"/>.
    /// </para>
    /// </remarks>
    public static string EntryAssemblyLocation
    {
      get
      {
        if (entryAssemblyLocation != null)
          return entryAssemblyLocation;
#if NETCF
        return entryAssemblyLocation = SystemInfo.NativeEntryAssemblyLocation;
#elif NETSTANDARD1_3 // TODO GetEntryAssembly is available for netstandard1.5
        return entryAssemblyLocation = AppContext.BaseDirectory;
#else
        return entryAssemblyLocation = Assembly.GetEntryAssembly()?.Location
          ?? throw new InvalidOperationException($"Unable to determine EntryAssembly location: EntryAssembly is null. Try explicitly setting {nameof(SystemInfo)}.{nameof(EntryAssemblyLocation)}");
#endif
      }
      set => entryAssemblyLocation = value;
    }

    /// <summary>
    /// Gets the ID of the current thread.
    /// </summary>
    /// <value>The ID of the current thread.</value>
    /// <remarks>
    /// <para>
    /// On the .NET framework, the <c>AppDomain.GetCurrentThreadId</c> method
    /// is used to obtain the thread ID for the current thread. This is the 
    /// operating system ID for the thread.
    /// </para>
    /// <para>
    /// On the .NET Compact Framework 1.0 it is not possible to get the 
    /// operating system thread ID for the current thread. The native method 
    /// <c>GetCurrentThreadId</c> is implemented inline in a header file
    /// and cannot be called.
    /// </para>
    /// <para>
    /// On the .NET Framework 2.0 the <c>Thread.ManagedThreadId</c> is used as this
    /// gives a stable id unrelated to the operating system thread ID which may 
    /// change if the runtime is using fibers.
    /// </para>
    /// </remarks>
    public static int CurrentThreadId
    {
      get
      {
#if NETCF_1_0
        return System.Threading.Thread.CurrentThread.GetHashCode();
#elif NET_2_0 || NETCF_2_0 || MONO_2_0 || MONO_3_5 || MONO_4_0 || NETSTANDARD
        return System.Threading.Thread.CurrentThread.ManagedThreadId;
#else
        return AppDomain.GetCurrentThreadId();
#endif
      }
    }

    /// <summary>
    /// Get the host name or machine name for the current machine
    /// </summary>
    /// <value>
    /// The hostname or machine name
    /// </value>
    /// <remarks>
    /// <para>
    /// Get the host name or machine name for the current machine
    /// </para>
    /// <para>
    /// The host name (<see cref="System.Net.Dns.GetHostName"/>) or
    /// the machine name (<c>Environment.MachineName</c>) for
    /// the current machine, or if neither of these are available
    /// then <c>NOT AVAILABLE</c> is returned.
    /// </para>
    /// </remarks>
    public static string HostName
    {
      get
      {
        if (s_hostName == null)
        {

          // Get the DNS host name of the current machine
          try
          {
            // Lookup the host name
            s_hostName = System.Net.Dns.GetHostName();
          }
          catch (System.Net.Sockets.SocketException)
          {
            LogLog.Debug(declaringType, "Socket exception occurred while getting the dns hostname. Error Ignored.");
          }
          catch (System.Security.SecurityException)
          {
            // We may get a security exception looking up the hostname
            // You must have Unrestricted DnsPermission to access resource
            LogLog.Debug(declaringType, "Security exception occurred while getting the dns hostname. Error Ignored.");
          }
          catch (Exception ex)
          {
            LogLog.Debug(declaringType, "Some other exception occurred while getting the dns hostname. Error Ignored.", ex);
          }

          // Get the NETBIOS machine name of the current machine
          if (s_hostName == null || s_hostName.Length == 0)
          {
            try
            {
#if NETSTANDARD1_3
              s_hostName = Environment.GetEnvironmentVariable("COMPUTERNAME");
#elif (!SSCLI && !NETCF)
              s_hostName = Environment.MachineName;
#endif
            }
            catch (InvalidOperationException)
            {
            }
            catch (System.Security.SecurityException)
            {
              // We may get a security exception looking up the machine name
              // You must have Unrestricted EnvironmentPermission to access resource
            }
          }

          // Couldn't find a value
          if (s_hostName == null || s_hostName.Length == 0)
          {
            s_hostName = s_notAvailableText;
            LogLog.Debug(declaringType, "Could not determine the hostname. Error Ignored. Empty host name will be used");
          }
        }
        return s_hostName;
      }
    }

    /// <summary>
    /// Get this application's friendly name
    /// </summary>
    /// <value>
    /// The friendly name of this application as a string
    /// </value>
    /// <remarks>
    /// <para>
    /// If available the name of the application is retrieved from
    /// the <c>AppDomain</c> using <c>AppDomain.CurrentDomain.FriendlyName</c>.
    /// </para>
    /// <para>
    /// Otherwise the file name of the entry assembly is used.
    /// </para>
    /// </remarks>
    public static string ApplicationFriendlyName
    {
      get
      {
        if (s_appFriendlyName == null)
        {
          try
          {
#if !NETCF && !NETSTANDARD1_3
            s_appFriendlyName = AppDomain.CurrentDomain.FriendlyName;
#endif
          }
          catch (System.Security.SecurityException)
          {
            // This security exception will occur if the caller does not have 
            // some undefined set of SecurityPermission flags.
            LogLog.Debug(declaringType, "Security exception while trying to get current domain friendly name. Error Ignored.");
          }

          if (s_appFriendlyName == null || s_appFriendlyName.Length == 0)
          {
            try
            {
              string assemblyLocation = SystemInfo.EntryAssemblyLocation;
              s_appFriendlyName = System.IO.Path.GetFileName(assemblyLocation);
            }
            catch (System.Security.SecurityException)
            {
              // Caller needs path discovery permission
            }
          }

          if (s_appFriendlyName == null || s_appFriendlyName.Length == 0)
          {
            s_appFriendlyName = s_notAvailableText;
          }
        }
        return s_appFriendlyName;
      }
    }

    /// <summary>
    /// Get the start time for the current process.
    /// </summary>
    /// <remarks>
    /// <para>
    /// This is the time at which the log4net library was loaded into the
    /// AppDomain. Due to reports of a hang in the call to <c>System.Diagnostics.Process.StartTime</c>
    /// this is not the start time for the current process.
    /// </para>
    /// <para>
    /// The log4net library should be loaded by an application early during its
    /// startup, therefore this start time should be a good approximation for
    /// the actual start time.
    /// </para>
    /// <para>
    /// Note that AppDomains may be loaded and unloaded within the
    /// same process without the process terminating, however this start time
    /// will be set per AppDomain.
    /// </para>
    /// </remarks>
    [Obsolete("Use ProcessStartTimeUtc and convert to local time if needed.")]
    public static DateTime ProcessStartTime
    {
      get { return s_processStartTimeUtc.ToLocalTime(); }
    }

    /// <summary>
    /// Get the UTC start time for the current process.
    /// </summary>
    /// <remarks>
    /// <para>
    /// This is the UTC time at which the log4net library was loaded into the
    /// AppDomain. Due to reports of a hang in the call to <c>System.Diagnostics.Process.StartTime</c>
    /// this is not the start time for the current process.
    /// </para>
    /// <para>
    /// The log4net library should be loaded by an application early during its
    /// startup, therefore this start time should be a good approximation for
    /// the actual start time.
    /// </para>
    /// <para>
    /// Note that AppDomains may be loaded and unloaded within the
    /// same process without the process terminating, however this start time
    /// will be set per AppDomain.
    /// </para>
    /// </remarks>
    public static DateTime ProcessStartTimeUtc
    {
      get { return s_processStartTimeUtc; }
    }

    /// <summary>
    /// Text to output when a <c>null</c> is encountered.
    /// </summary>
    /// <remarks>
    /// <para>
    /// Use this value to indicate a <c>null</c> has been encountered while
    /// outputting a string representation of an item.
    /// </para>
    /// <para>
    /// The default value is <c>(null)</c>. This value can be overridden by specifying
    /// a value for the <c>log4net.NullText</c> appSetting in the application's
    /// .config file.
    /// </para>
    /// </remarks>
    public static string NullText
    {
      get { return s_nullText; }
      set { s_nullText = value; }
    }

    /// <summary>
    /// Text to output when an unsupported feature is requested.
    /// </summary>
    /// <remarks>
    /// <para>
    /// Use this value when an unsupported feature is requested.
    /// </para>
    /// <para>
    /// The default value is <c>NOT AVAILABLE</c>. This value can be overridden by specifying
    /// a value for the <c>log4net.NotAvailableText</c> appSetting in the application's
    /// .config file.
    /// </para>
    /// </remarks>
    public static string NotAvailableText
    {
      get { return s_notAvailableText; }
      set { s_notAvailableText = value; }
    }

    #endregion Public Static Properties

    #region Public Static Methods

    /// <summary>
    /// Gets the assembly location path for the specified assembly.
    /// </summary>
    /// <param name="myAssembly">The assembly to get the location for.</param>
    /// <returns>The location of the assembly.</returns>
    /// <remarks>
    /// <para>
    /// This method does not guarantee to return the correct path
    /// to the assembly. If only tries to give an indication as to
    /// where the assembly was loaded from.
    /// </para>
    /// </remarks>
    public static string AssemblyLocationInfo(Assembly myAssembly)
    {
#if NETCF
      return "Not supported on Microsoft .NET Compact Framework";
#elif NETSTANDARD1_3
            return "Not supported on .NET Core";
#else
      if (myAssembly.GlobalAssemblyCache)
      {
        return "Global Assembly Cache";
      }
      else
      {
        try
        {
#if NET_4_0 || MONO_4_0
          if (myAssembly.IsDynamic)
          {
            return "Dynamic Assembly";
          }
#else
#if !NETSTANDARD2_0
          if (myAssembly is System.Reflection.Emit.AssemblyBuilder)
          {
            return "Dynamic Assembly";
          }
#endif

          if (myAssembly.GetType().FullName == "System.Reflection.Emit.InternalAssemblyBuilder")
          {
            return "Dynamic Assembly";
          }
#endif
          else
          {
            // This call requires FileIOPermission for access to the path
            // if we don't have permission then we just ignore it and
            // carry on.
            return myAssembly.Location;
          }
        }
        catch (NotSupportedException)
        {
          // The location information may be unavailable for dynamic assemblies and a NotSupportedException
          // is thrown in those cases. See: http://msdn.microsoft.com/de-de/library/system.reflection.assembly.location.aspx
          return "Dynamic Assembly";
        }
        catch (TargetInvocationException ex)
        {
          return "Location Detect Failed (" + ex.Message + ")";
        }
        catch (ArgumentException ex)
        {
          return "Location Detect Failed (" + ex.Message + ")";
        }
        catch (System.Security.SecurityException)
        {
          return "Location Permission Denied";
        }
      }
#endif
    }

    /// <summary>
    /// Gets the fully qualified name of the <see cref="Type" />, including 
    /// the name of the assembly from which the <see cref="Type" /> was 
    /// loaded.
    /// </summary>
    /// <param name="type">The <see cref="Type" /> to get the fully qualified name for.</param>
    /// <returns>The fully qualified name for the <see cref="Type" />.</returns>
    /// <remarks>
    /// <para>
    /// This is equivalent to the <c>Type.AssemblyQualifiedName</c> property,
    /// but this method works on the .NET Compact Framework 1.0 as well as
    /// the full .NET runtime.
    /// </para>
    /// </remarks>
    public static string AssemblyQualifiedName(Type type)
    {
      return type.FullName + ", "
#if NETSTANDARD1_3
        + type.GetTypeInfo().Assembly.FullName;
#else
        + type.Assembly.FullName;
#endif
    }

    /// <summary>
    /// Gets the short name of the <see cref="Assembly" />.
    /// </summary>
    /// <param name="myAssembly">The <see cref="Assembly" /> to get the name for.</param>
    /// <returns>The short name of the <see cref="Assembly" />.</returns>
    /// <remarks>
    /// <para>
    /// The short name of the assembly is the <see cref="Assembly.FullName" /> 
    /// without the version, culture, or public key. i.e. it is just the 
    /// assembly's file name without the extension.
    /// </para>
    /// <para>
    /// Use this rather than <c>Assembly.GetName().Name</c> because that
    /// is not available on the Compact Framework.
    /// </para>
    /// <para>
    /// Because of a FileIOPermission security demand we cannot do
    /// the obvious Assembly.GetName().Name. We are allowed to get
    /// the <see cref="Assembly.FullName" /> of the assembly so we 
    /// start from there and strip out just the assembly name.
    /// </para>
    /// </remarks>
    public static string AssemblyShortName(Assembly myAssembly)
    {
      string name = myAssembly.FullName;
      int offset = name.IndexOf(',');
      if (offset > 0)
      {
        name = name.Substring(0, offset);
      }
      return name.Trim();

      // TODO: Do we need to unescape the assembly name string? 
      // Doc says '\' is an escape char but has this already been 
      // done by the string loader?
    }

    /// <summary>
    /// Gets the file name portion of the <see cref="Assembly" />, including the extension.
    /// </summary>
    /// <param name="myAssembly">The <see cref="Assembly" /> to get the file name for.</param>
    /// <returns>The file name of the assembly.</returns>
    /// <remarks>
    /// <para>
    /// Gets the file name portion of the <see cref="Assembly" />, including the extension.
    /// </para>
    /// </remarks>
    public static string AssemblyFileName(Assembly myAssembly)
    {
#if NETCF || NETSTANDARD1_3 // TODO Assembly.Location is in netstandard1.5 System.Reflection
      // This is not very good because it assumes that only
      // the entry assembly can be an EXE. In fact multiple
      // EXEs can be loaded in to a process.

      string assemblyShortName = SystemInfo.AssemblyShortName(myAssembly);
      string entryAssemblyShortName = System.IO.Path.GetFileNameWithoutExtension(SystemInfo.EntryAssemblyLocation);

      if (string.Compare(assemblyShortName, entryAssemblyShortName, true) == 0)
      {
        // assembly is entry assembly
        return assemblyShortName + ".exe";
      }
      else
      {
        // assembly is not entry assembly
        return assemblyShortName + ".dll";
      }
#else
      return System.IO.Path.GetFileName(myAssembly.Location);
#endif
    }

    /// <summary>
    /// Loads the type specified in the type string.
    /// </summary>
    /// <param name="relativeType">A sibling type to use to load the type.</param>
    /// <param name="typeName">The name of the type to load.</param>
    /// <param name="throwOnError">Flag set to <c>true</c> to throw an exception if the type cannot be loaded.</param>
    /// <param name="ignoreCase"><c>true</c> to ignore the case of the type name; otherwise, <c>false</c></param>
    /// <returns>The type loaded or <c>null</c> if it could not be loaded.</returns>
    /// <remarks>
    /// <para>
    /// If the type name is fully qualified, i.e. if contains an assembly name in 
    /// the type name, the type will be loaded from the system using 
    /// <see cref="M:Type.GetType(string,bool)"/>.
    /// </para>
    /// <para>
    /// If the type name is not fully qualified, it will be loaded from the assembly
    /// containing the specified relative type. If the type is not found in the assembly 
    /// then all the loaded assemblies will be searched for the type.
    /// </para>
    /// </remarks>
    public static Type GetTypeFromString(Type relativeType, string typeName, bool throwOnError, bool ignoreCase)
    {
#if NETSTANDARD1_3
      return GetTypeFromString(relativeType.GetTypeInfo().Assembly, typeName, throwOnError, ignoreCase);
#else
      return GetTypeFromString(relativeType.Assembly, typeName, throwOnError, ignoreCase);
#endif
    }

#if !NETSTANDARD1_3
    /// <summary>
    /// Loads the type specified in the type string.
    /// </summary>
    /// <param name="typeName">The name of the type to load.</param>
    /// <param name="throwOnError">Flag set to <c>true</c> to throw an exception if the type cannot be loaded.</param>
    /// <param name="ignoreCase"><c>true</c> to ignore the case of the type name; otherwise, <c>false</c></param>
    /// <returns>The type loaded or <c>null</c> if it could not be loaded.</returns>    
    /// <remarks>
    /// <para>
    /// If the type name is fully qualified, i.e. if contains an assembly name in 
    /// the type name, the type will be loaded from the system using 
    /// <see cref="M:Type.GetType(string,bool)"/>.
    /// </para>
    /// <para>
    /// If the type name is not fully qualified it will be loaded from the
    /// assembly that is directly calling this method. If the type is not found 
    /// in the assembly then all the loaded assemblies will be searched for the type.
    /// </para>
    /// </remarks>
    public static Type GetTypeFromString(string typeName, bool throwOnError, bool ignoreCase)
    {
      return GetTypeFromString(Assembly.GetCallingAssembly(), typeName, throwOnError, ignoreCase);
    }
#endif

    /// <summary>
    /// Loads the type specified in the type string.
    /// </summary>
    /// <param name="relativeAssembly">An assembly to load the type from.</param>
    /// <param name="typeName">The name of the type to load.</param>
    /// <param name="throwOnError">Flag set to <c>true</c> to throw an exception if the type cannot be loaded.</param>
    /// <param name="ignoreCase"><c>true</c> to ignore the case of the type name; otherwise, <c>false</c></param>
    /// <returns>The type loaded or <c>null</c> if it could not be loaded.</returns>
    /// <remarks>
    /// <para>
    /// If the type name is fully qualified, i.e. if contains an assembly name in 
    /// the type name, the type will be loaded from the system using 
    /// <see cref="M:Type.GetType(string,bool)"/>.
    /// </para>
    /// <para>
    /// If the type name is not fully qualified it will be loaded from the specified
    /// assembly. If the type is not found in the assembly then all the loaded assemblies 
    /// will be searched for the type.
    /// </para>
    /// </remarks>
    public static Type GetTypeFromString(Assembly relativeAssembly, string typeName, bool throwOnError, bool ignoreCase)
    {
      // Check if the type name specifies the assembly name
      if (typeName.IndexOf(',') == -1)
      {
        //LogLog.Debug(declaringType, "SystemInfo: Loading type ["+typeName+"] from assembly ["+relativeAssembly.FullName+"]");
#if NETSTANDARD1_3
        return relativeAssembly.GetType(typeName, throwOnError, ignoreCase);
#elif NETCF
        return relativeAssembly.GetType(typeName, throwOnError);
#else
        // Attempt to lookup the type from the relativeAssembly
        Type type = relativeAssembly.GetType(typeName, false, ignoreCase);
        if (type != null)
        {
          // Found type in relative assembly
          //LogLog.Debug(declaringType, "SystemInfo: Loaded type ["+typeName+"] from assembly ["+relativeAssembly.FullName+"]");
          return type;
        }

        Assembly[] loadedAssemblies = null;
        try
        {
          loadedAssemblies = AppDomain.CurrentDomain.GetAssemblies();
        }
        catch (System.Security.SecurityException)
        {
          // Insufficient permissions to get the list of loaded assemblies
        }

        if (loadedAssemblies != null)
        {
          Type fallback = null;
          // Search the loaded assemblies for the type
          foreach (Assembly assembly in loadedAssemblies)
          {
            Type t = assembly.GetType(typeName, false, ignoreCase);
            if (t != null)
            {
              // Found type in loaded assembly
              LogLog.Debug(declaringType, "Loaded type [" + typeName + "] from assembly [" + assembly.FullName + "] by searching loaded assemblies.");
              if (assembly.GlobalAssemblyCache)
              {
                fallback = t;
              }
              else
              {
                return t;
              }
            }
          }
          if (fallback != null)
          {
            return fallback;
          }
        }

        // Didn't find the type
        if (throwOnError)
        {
          throw new TypeLoadException("Could not load type [" + typeName + "]. Tried assembly [" + relativeAssembly.FullName + "] and all loaded assemblies");
        }
        return null;
#endif
      }
      else
      {
        // Includes explicit assembly name
        //LogLog.Debug(declaringType, "SystemInfo: Loading type ["+typeName+"] from global Type");

#if NETCF
        // In NETCF 2 and 3 arg versions seem to behave differently
        // https://issues.apache.org/jira/browse/LOG4NET-113
        return Type.GetType(typeName, throwOnError);
#else
        return Type.GetType(typeName, throwOnError, ignoreCase);
#endif
      }
    }


    /// <summary>
    /// Generate a new guid
    /// </summary>
    /// <returns>A new Guid</returns>
    /// <remarks>
    /// <para>
    /// Generate a new guid
    /// </para>
    /// </remarks>
    public static Guid NewGuid()
    {
#if NETCF_1_0
      return PocketGuid.NewGuid();
#else
      return Guid.NewGuid();
#endif
    }

    /// <summary>
    /// Create an <see cref="ArgumentOutOfRangeException"/>
    /// </summary>
    /// <param name="parameterName">The name of the parameter that caused the exception</param>
    /// <param name="actualValue">The value of the argument that causes this exception</param>
    /// <param name="message">The message that describes the error</param>
    /// <returns>the ArgumentOutOfRangeException object</returns>
    /// <remarks>
    /// <para>
    /// Create a new instance of the <see cref="ArgumentOutOfRangeException"/> class 
    /// with a specified error message, the parameter name, and the value 
    /// of the argument.
    /// </para>
    /// <para>
    /// The Compact Framework does not support the 3 parameter constructor for the
    /// <see cref="ArgumentOutOfRangeException"/> type. This method provides an
    /// implementation that works for all platforms.
    /// </para>
    /// </remarks>
    public static ArgumentOutOfRangeException CreateArgumentOutOfRangeException(string parameterName, object actualValue, string message)
    {
#if NETCF_1_0
      return new ArgumentOutOfRangeException(message + " [param=" + parameterName + "] [value=" + actualValue + "]");
#elif NETCF_2_0
      return new ArgumentOutOfRangeException(parameterName, message + " [value=" + actualValue + "]");
#else
      return new ArgumentOutOfRangeException(parameterName, actualValue, message);
#endif
    }


    /// <summary>
    /// Parse a string into an <see cref="Int32"/> value
    /// </summary>
    /// <param name="s">the string to parse</param>
    /// <param name="val">out param where the parsed value is placed</param>
    /// <returns><c>true</c> if the string was able to be parsed into an integer</returns>
    /// <remarks>
    /// <para>
    /// Attempts to parse the string into an integer. If the string cannot
    /// be parsed then this method returns <c>false</c>. The method does not throw an exception.
    /// </para>
    /// </remarks>
    public static bool TryParse(string s, out int val)
    {
#if NETCF
      val = 0;
      try
      {
        val = int.Parse(s, System.Globalization.NumberStyles.Integer, System.Globalization.CultureInfo.InvariantCulture);
        return true;
      }
      catch
      {
      }

      return false;
#else
      // Initialise out param
      val = 0;

      try
      {
        double doubleVal;
        if (Double.TryParse(s, System.Globalization.NumberStyles.Integer, System.Globalization.CultureInfo.InvariantCulture, out doubleVal))
        {
          val = Convert.ToInt32(doubleVal);
          return true;
        }
      }
      catch
      {
        // Ignore exception, just return false
      }

      return false;
#endif
    }

    /// <summary>
    /// Parse a string into an <see cref="Int64"/> value
    /// </summary>
    /// <param name="s">the string to parse</param>
    /// <param name="val">out param where the parsed value is placed</param>
    /// <returns><c>true</c> if the string was able to be parsed into an integer</returns>
    /// <remarks>
    /// <para>
    /// Attempts to parse the string into an integer. If the string cannot
    /// be parsed then this method returns <c>false</c>. The method does not throw an exception.
    /// </para>
    /// </remarks>
    public static bool TryParse(string s, out long val)
    {
#if NETCF
      val = 0;
      try
      {
        val = long.Parse(s, System.Globalization.NumberStyles.Integer, System.Globalization.CultureInfo.InvariantCulture);
        return true;
      }
      catch
      {
      }

      return false;
#else
      // Initialise out param
      val = 0;

      try
      {
        double doubleVal;
        if (Double.TryParse(s, System.Globalization.NumberStyles.Integer, System.Globalization.CultureInfo.InvariantCulture, out doubleVal))
        {
          val = Convert.ToInt64(doubleVal);
          return true;
        }
      }
      catch
      {
        // Ignore exception, just return false
      }

      return false;
#endif
    }

    /// <summary>
    /// Parse a string into an <see cref="Int16"/> value
    /// </summary>
    /// <param name="s">the string to parse</param>
    /// <param name="val">out param where the parsed value is placed</param>
    /// <returns><c>true</c> if the string was able to be parsed into an integer</returns>
    /// <remarks>
    /// <para>
    /// Attempts to parse the string into an integer. If the string cannot
    /// be parsed then this method returns <c>false</c>. The method does not throw an exception.
    /// </para>
    /// </remarks>
    public static bool TryParse(string s, out short val)
    {
#if NETCF
      val = 0;
      try
      {
        val = short.Parse(s, System.Globalization.NumberStyles.Integer, System.Globalization.CultureInfo.InvariantCulture);
        return true;
      }
      catch
      {
      }

      return false;
#else
      // Initialise out param
      val = 0;

      try
      {
        double doubleVal;
        if (Double.TryParse(s, System.Globalization.NumberStyles.Integer, System.Globalization.CultureInfo.InvariantCulture, out doubleVal))
        {
          val = Convert.ToInt16(doubleVal);
          return true;
        }
      }
      catch
      {
        // Ignore exception, just return false
      }

      return false;
#endif
    }

    /// <summary>
    /// Lookup an application setting
    /// </summary>
    /// <param name="key">the application settings key to lookup</param>
    /// <returns>the value for the key, or <c>null</c></returns>
    /// <remarks>
    /// <para>
    /// Configuration APIs are not supported under the Compact Framework
    /// </para>
    /// </remarks>
    public static string GetAppSetting(string key)
    {
      try
      {
#if NETCF || NETSTANDARD1_3
        // Configuration APIs are not suported under the Compact Framework
#elif NET_2_0 || NETSTANDARD2_0
        return ConfigurationManager.AppSettings[key];
#else
        return ConfigurationSettings.AppSettings[key];
#endif
      }
      catch (Exception ex)
      {
        // If an exception is thrown here then it looks like the config file does not parse correctly.
        LogLog.Error(declaringType, "Exception while reading ConfigurationSettings. Check your .config file is well formed XML.", ex);
      }
      return null;
    }

    /// <summary>
    /// Convert a path into a fully qualified local file path.
    /// </summary>
    /// <param name="path">The path to convert.</param>
    /// <returns>The fully qualified path.</returns>
    /// <remarks>
    /// <para>
    /// Converts the path specified to a fully
    /// qualified path. If the path is relative it is
    /// taken as relative from the application base 
    /// directory.
    /// </para>
    /// <para>
    /// The path specified must be a local file path, a URI is not supported.
    /// </para>
    /// </remarks>
    public static string ConvertToFullPath(string path)
    {
      if (path == null)
      {
        throw new ArgumentNullException("path");
      }

      string baseDirectory = "";
      try
      {
        string applicationBaseDirectory = SystemInfo.ApplicationBaseDirectory;
        if (applicationBaseDirectory != null)
        {
          // applicationBaseDirectory may be a URI not a local file path
          Uri applicationBaseDirectoryUri = new Uri(applicationBaseDirectory);
          if (applicationBaseDirectoryUri.IsFile)
          {
            baseDirectory = applicationBaseDirectoryUri.LocalPath;
          }
        }
      }
      catch
      {
        // Ignore URI exceptions & SecurityExceptions from SystemInfo.ApplicationBaseDirectory
      }

      if (baseDirectory != null && baseDirectory.Length > 0)
      {
        // Note that Path.Combine will return the second path if it is rooted
        return Path.GetFullPath(Path.Combine(baseDirectory, path));
      }
      return Path.GetFullPath(path);
    }

    /// <summary>
    /// Creates a new case-insensitive instance of the <see cref="Hashtable"/> class with the default initial capacity. 
    /// </summary>
    /// <returns>A new case-insensitive instance of the <see cref="Hashtable"/> class with the default initial capacity</returns>
    /// <remarks>
    /// <para>
    /// The new Hashtable instance uses the default load factor, the CaseInsensitiveHashCodeProvider, and the CaseInsensitiveComparer.
    /// </para>
    /// </remarks>
    public static Hashtable CreateCaseInsensitiveHashtable()
    {
#if NETCF_1_0
      return new Hashtable(CaseInsensitiveHashCodeProvider.Default, CaseInsensitiveComparer.Default);
#elif NETCF_2_0 || NET_2_0 || MONO_2_0 || MONO_3_5 || MONO_4_0
      return new Hashtable(StringComparer.OrdinalIgnoreCase);
#else
      return System.Collections.Specialized.CollectionsUtil.CreateCaseInsensitiveHashtable();
#endif
    }

    /// <summary>
    /// Tests two strings for equality, the ignoring case.
    /// </summary>
    /// <remarks>
    /// If the platform permits, culture information is ignored completely (ordinal comparison).
    /// The aim of this method is to provide a fast comparison that deals with <c>null</c> and ignores different casing.
    /// It is not supposed to deal with various, culture-specific habits.
    /// Use it to compare against pure ASCII constants, like keywords etc.
    /// </remarks>
    /// <param name="a">The one string.</param>
    /// <param name="b">The other string.</param>
    /// <returns><c>true</c> if the strings are equal, <c>false</c> otherwise.</returns>
    public static Boolean EqualsIgnoringCase(String a, String b)
    {
#if NET_1_0 || NET_1_1 || NETCF_1_0
            return string.Compare(a, b, true, System.Globalization.CultureInfo.InvariantCulture) == 0
#elif NETSTANDARD1_3
            return CultureInfo.InvariantCulture.CompareInfo.Compare(a, b, CompareOptions.IgnoreCase) == 0;
#else // >= .NET-2.0
      return String.Equals(a, b, StringComparison.OrdinalIgnoreCase);
#endif
    }

    #endregion Public Static Methods

    #region Private Static Methods

#if NETCF
    private static string NativeEntryAssemblyLocation 
    {
      get 
      {
        StringBuilder moduleName = null;

        IntPtr moduleHandle = GetModuleHandle(IntPtr.Zero);

        if (moduleHandle != IntPtr.Zero) 
        {
          moduleName = new StringBuilder(255);
          if (GetModuleFileName(moduleHandle, moduleName,  moduleName.Capacity) == 0) 
          {
            throw new NotSupportedException(NativeError.GetLastError().ToString());
          }
        } 
        else 
        {
          throw new NotSupportedException(NativeError.GetLastError().ToString());
        }

        return moduleName.ToString();
      }
    }

    [DllImport("CoreDll.dll", SetLastError=true, CharSet=CharSet.Unicode)]
    private static extern IntPtr GetModuleHandle(IntPtr ModuleName);

    [DllImport("CoreDll.dll", SetLastError=true, CharSet=CharSet.Unicode)]
    private static extern Int32 GetModuleFileName(
      IntPtr hModule,
      StringBuilder ModuleName,
      Int32 cch);

#endif

    #endregion Private Static Methods

    #region Public Static Fields

    /// <summary>
    /// Gets an empty array of types.
    /// </summary>
    /// <remarks>
    /// <para>
    /// The <c>Type.EmptyTypes</c> field is not available on
    /// the .NET Compact Framework 1.0.
    /// </para>
    /// </remarks>
    public static readonly Type[] EmptyTypes = new Type[0];

    #endregion Public Static Fields

    #region Private Static Fields

    /// <summary>
    /// The fully qualified type of the SystemInfo class.
    /// </summary>
    /// <remarks>
    /// Used by the internal logger to record the Type of the
    /// log message.
    /// </remarks>
    private static readonly Type declaringType = typeof(SystemInfo);

    /// <summary>
    /// Cache the host name for the current machine
    /// </summary>
    private static string s_hostName;

    /// <summary>
    /// Cache the application friendly name
    /// </summary>
    private static string s_appFriendlyName;

    /// <summary>
    /// Text to output when a <c>null</c> is encountered.
    /// </summary>
    private static string s_nullText;

    /// <summary>
    /// Text to output when an unsupported feature is requested.
    /// </summary>
    private static string s_notAvailableText;

    /// <summary>
    /// Start time for the current process.
    /// </summary>
    private static DateTime s_processStartTimeUtc = DateTime.UtcNow;

    #endregion

    #region Compact Framework Helper Classes
#if NETCF_1_0
    /// <summary>
    /// Generate GUIDs on the .NET Compact Framework.
    /// </summary>
    public class PocketGuid
    {
      // guid variant types
      private enum GuidVariant
      {
        ReservedNCS = 0x00,
        Standard = 0x02,
        ReservedMicrosoft = 0x06,
        ReservedFuture = 0x07
      }

      // guid version types
      private enum GuidVersion
      {
        TimeBased = 0x01,
        Reserved = 0x02,
        NameBased = 0x03,
        Random = 0x04
      }

      // constants that are used in the class
      private class Const
      {
        // number of bytes in guid
        public const int ByteArraySize = 16;

        // multiplex variant info
        public const int VariantByte = 8;
        public const int VariantByteMask = 0x3f;
        public const int VariantByteShift = 6;

        // multiplex version info
        public const int VersionByte = 7;
        public const int VersionByteMask = 0x0f;
        public const int VersionByteShift = 4;
      }

      // imports for the crypto api functions
      private class WinApi
      {
        public const uint PROV_RSA_FULL = 1;
        public const uint CRYPT_VERIFYCONTEXT = 0xf0000000;

        [DllImport("CoreDll.dll")] 
        public static extern bool CryptAcquireContext(
          ref IntPtr phProv, string pszContainer, string pszProvider,
          uint dwProvType, uint dwFlags);

        [DllImport("CoreDll.dll")] 
        public static extern bool CryptReleaseContext( 
          IntPtr hProv, uint dwFlags);

        [DllImport("CoreDll.dll")] 
        public static extern bool CryptGenRandom(
          IntPtr hProv, int dwLen, byte[] pbBuffer);
      }

      // all static methods
      private PocketGuid()
      {
      }

      /// <summary>
      /// Return a new System.Guid object.
      /// </summary>
      public static Guid NewGuid()
      {
        IntPtr hCryptProv = IntPtr.Zero;
        Guid guid = Guid.Empty;

        try
        {
          // holds random bits for guid
          byte[] bits = new byte[Const.ByteArraySize];

          // get crypto provider handle
          if (!WinApi.CryptAcquireContext(ref hCryptProv, null, null, 
            WinApi.PROV_RSA_FULL, WinApi.CRYPT_VERIFYCONTEXT))
          {
            throw new SystemException(
              "Failed to acquire cryptography handle.");
          }

          // generate a 128 bit (16 byte) cryptographically random number
          if (!WinApi.CryptGenRandom(hCryptProv, bits.Length, bits))
          {
            throw new SystemException(
              "Failed to generate cryptography random bytes.");
          }

          // set the variant
          bits[Const.VariantByte] &= Const.VariantByteMask;
          bits[Const.VariantByte] |= 
            ((int)GuidVariant.Standard << Const.VariantByteShift);

          // set the version
          bits[Const.VersionByte] &= Const.VersionByteMask;
          bits[Const.VersionByte] |= 
            ((int)GuidVersion.Random << Const.VersionByteShift);

          // create the new System.Guid object
          guid = new Guid(bits);
        }
        finally
        {
          // release the crypto provider handle
          if (hCryptProv != IntPtr.Zero)
            WinApi.CryptReleaseContext(hCryptProv, 0);
        }

        return guid;
      }
    }
#endif
    #endregion Compact Framework Helper Classes
  }
}
